The present invention relates to novel microorganism strains decomposing tetramethyl ammonium hydroxide; TMAH) and wastewater treatment method by applying the above strains.
More particularly, the present invention relates to novel strains decomposing tetramethyl ammonium hydroxide which is utilized for etching the surface of silicon chip while manufacturing semiconductors and is toxic and hard to be degraded. In addition, the present invention relates to wastewater treatment method which comprises applying the above strains into TMAHxe2x80x94containing wastewater and then performing batch culture or various kinds of continuous culture for purging the wastewater.
Recently, internet and information technology (IT) industries have been developed and the semiconductor demand also increased explosively. However, the development of the semiconductor industry induces the use of chemical substance gradually. Precisely, tetramethyl ammonium hydroxide (TMAH) which is utilized for etching the surface of silicone chip while manufacturing semiconductors has been exhausted in increased amounts.
TMAH is very toxic (toxicity LC50=460 ppm) and cannot be biodegraded easily. Hence, TMAH makes biological oxygen demand (BOD) fluctuate extremely in the wastewater treatment facilities of semiconductor manufacturing plant. Therefore, the removal of TMAH from industrial wastewater has become a very important issue in order to protect environment.
Presently, some treatment method has been disclosed for eliminating TMAH from wastewater. In detail, concentration method that comprises concentrating TMAH from the wastewater by using ion exchange resin column, ultra filtration (UF) or reverse osmosis (RO), and disposing TMAH, has been reported. In addition, super-critical treatment method that comprises burning the concentrated TMAH has been demonstrated. Unfortunately, such traditional treatment methods require complicated processes and provokes secondary contamination problems accompanied the said concentration or combustion.
Therefore, more economical and efficient processes for treating TMAH should be developed in order to satisfy the increasing need of environment protection.
To overcome the foregoing and other disadvantages, we, the inventors of the present invention, have developed biological treatment processes which can decompose and eliminate TMAH efficiently even in mild conditions. First, novel microorganism strains which were insensitive to TMAH and utilized TMAH as a sole carbon and energy source have been separated. In addition, we have confirmed that the above strains could reduce the biological oxygen demand (BOD) remarkably when the strains is applied to wastewater containing TMAH.
The object of the present invention is to provide novel microorganism strains that can degrade tetramethyl ammonium hydroxide (TMAH).
Further object of the present invention is to provide biological treatment methods for TMAH containing wastewater by applying the said strains.
The present invention provides novel microorganism strains capable of decomposing tetramethyl ammonium hydroxide (TMAH), which is often utilized in etching the surface of silicone chip and, is toxic and hard to be degraded. In addition, the present invention provides TMAH containing wastewater treatment methods using the above strains.
The microorganism strains of the present invention is separated and identified by the process comprising steps as follows.
Wastewater sample is obtained from the domestic factory manufacturing semiconductors and is inoculated into the nutrient culture medium for enriching the microorganism of said wastewater primarily. Then, the strains grown above are again cultivated on the Nutrient culture medium containing TMAH. 7 strains out of the above are separated according to the cell survival, namely insensibility to TMAH. In particular, 7 TMAH insensitive strains are first separated and then designated with IBN-H1xcx9cIBN-H7 respectively. Furthermore, three strains, IBN-H1, IBN-H4, IBN-H7 superior in decomposing TMAH, are selected among the above strains.
The 3 adopted strains, IBN-H1, IBN-H4, IBN-H7, are examined by BIOLOG system, MIDI, partial nucleotide sequence determination of 16s RNA and so on. As a result, the above strains are identified to be novel strains corresponding to Kluyveromyces delphensis, Bacillus cereus and Acinetobacter sp. respectively. The strains obtained above are named with Kluyveromyces delphensis IBN-H1, Bacillus cereus IBN-H4 and Acinetobacter sp. IBN-H7 respectively and have been deposited in the Korean Collection for Type Cultures (KCTC) of the Korean Research Institute of Bioscience and Biotechnology (KRIBB), an international deposit organization, #52, Oun-dong, Yusong-ku, Taejon 305-333, Republic of Korea on Jul. 18, 2000, and identified as KCTC accession numbers, KCTC 0834 BP, KCTC 0835 BP and KCTC 0836 BP.
It is confirmed that all the strains selected above can grow up to the OD value 0:2 in the minimal culture medium containing TMAH as a sole carbon source and essential mineral components. In addition, the strains can also grow in both 25xc2x0 C. and 30xc2x0 C. without variations and can grow well even in normal or weakly acidic condition.
The microorganism strains of the present invention are insensitive to TMAH and uses TMAH as a sole carbon source for cell growth. Hence, they are exploited in the biological wastewater treatment method for removing TMAH. In this process, one strain or more than one strains selected among the group comprising Kluyveromyces delphensis, Bacillus cereus and Acinetobacter sp. can be utilized in sole or mixed culture state, preferably.
The biological wastewater treatment process for removing TMAH of wastewater, which utilizes the microorganism strain of the present invention, can be performed by using the batch culture process. Preferably, the wastewater treatment process is performed by the fed-batch culture or the continuous culture for the efficiency and the continuation of the above process. In the continuous culture system, the microorganism strain is inoculated into a fermentation vessel containing the Nutrient culture medium and is cultivated by using the batch culture process until the density reaches certain point. For example, the OD value is above 0.15. Then wastewater containing TMAH become passed through at the definite dilution velocity.
In the mean time, whatever culture process is adopted, the above stains can be fixed onto a supporting carrier preferably. The carrier facilitates said processes since it enables the strains to be used repeatedly and to remove wastewater conveniently. The carrier substance can be selected preferably among alginate, urethane foam and so on, which are conventional material for the microorganism fixation.